Such a known apparatus, as described in Patent EP-A 0 172 557, comprises a driving shaft and a driven shaft, which are coaxial, a driving plate driven by the driving shaft, a driven plate fast with the driven shaft and bearing a continuous circular track eccentric with respect to the common axis of the driving and driven shafts, rollers which roll inside the circular track, each of these rollers being borne by a rod articulated, about a pivot axis, on the driving plate, the articulations of all the rods being uniformly distributed over a circle whose center lies on the common axis of the two coaxial shafts. Another known apparatus of this type comprises two independent assemblies of rollers, tracks, rods, articulations and driving plates, these two assemblies having eccentric axes diametrically opposite with respect to the common axis of the driving and driven shafts.
In these known apparatus, a diameter A,A' (FIG. 1) passing through axis 0 common to the driving and driven shafts and through axis 0' of the eccentric circular track determines, on this track, two semi-circumferences. In one semi-circumference A.A', the axis of each roller moves towards the axis 0 of the driving and driven shafts, whilst, in the other semi-circumference A'.A, the axis of each roller moves away from this axis 0. During the displacement between points A' and A, the roller undergoes an acceleration and an increase in its kinetic energy. Such acceleration is obtained by the driving force of the rod by the driving shaft and further to the angular position of the rod with respect to the tangent to the path determined by the track, this driving force has for its effect to reduce the centrifugal efforts of the roller in rotation on the semi-circumference A'A. On the contrary, during the displacement of point A to point A', along the opposite semi-circumference, the roller undergoes a deceleration and a reduction in its kinetic energy and likewise further to the angular position of the rod, such deceleration produces a thrust of the rod and an increase in the efforts of the rollers on the track when they rotate on this semi-circumference A.A'. The effects of such reductions of the efforts on the path A'.A and of such increases of the efforts on the path A.A' add up to exert on axis 0' of the track a torque which is transmitted to the driven shaft of axis 0. When the receiver begins to rotate then accelerates, the torques transmitted decrease as a function in particular of the difference in the speeds between the driving shaft and the receiver. This effect is translated by a reduction in the frequency of the accelerations and decelerations previously indicated. These torques tend towards a zero value when these speeds are equal and when the transmission ratio approaches 1/1, then they become negative and increasing when this ratio is less than 1/1.
Furthermore, when the motor rotates, the rollers are subjected to continuous centrifugal forces which are exerted in all directions around the common axis 0. These centrifugal forces produce positive torques on axis 0' during the path from A towards A' and negative ones during the path from A' towards A. It will be observed that, further to the angular position of the rods with respect to the track, the distribution of the number of the rollers and consequently of the active masses, is unequal between the two semi-circumferences A.A' and A'.A, these active masses being more numerous on the path of A towards A'. The positive torques transmitted in part A.A' are then always greater than the negative torques transmitted in part A'.A. As a result, even when the ratio of the speeds is 1/1 and when the torques due to the accelerations and decelerations no longer exist, torques due solely to the centrifugal forces and to the unequal distribution of the tollers are always transmitted, the importance of these torques being a function of the speed of the motor/receiver assembly.
The torques transmitted by the apparatus are in the first place the torques produced as a function of the increases and reductions in kinetic energy which are due, as explained previously, to the accelerations and decelerations of the rollers. These torques, which are the most important at start-up, decrease when the transmission ratio decreases and they tend towards a zero value on approaching the ratio 1/1. Moreover with the ratio 1/1, the torques are transmitted further to the unequal distribution of the number of rollers and the centrifugal forces between the semi-circumferences A.A' and A'.A.
This being so, any modification of the speeds and the driving torques reacts instantaneously on the transmission ratios and on the receiving torques and thus automatically adapts these different parameters to the operational conditions of the apparatus.
However, the heretofore known apparatus of this type present numerous drawbacks. In fact, as the rollers roll on the track, in numerous situations as a function of the centrifugal forces developed, the rollers leave the track and fall on the driving shaft and, when the centrifugal forces increase, sometimes suddenly, the rollers are then rejected against the track. This results in repeated shocks which damage these members of the apparatus. The rollers are not heavy enough to provide sufficiently powerful centrifugal forces and the eccentricities between axis 0' of the track and the central axis 0 are too reduced to give the apparatus great efficiency. The apparatus present a considerable volume especially when they comprise at least two assemblies of rollers, tracks and driving plates in order to be balanced.
An attentive examination of FIG. 1 will show that, in fact, the accelerations of the rollers in the semi-circumference A'A are produced only up to position A" located before position A, and the deceleration of the rollers effectively begins at position A" and continues, passing through A up to position A'. This zone of deceleration between A" and A unfortunately produces negative torques on axis 0' of the track, which cause part of the effect of the positive torques produced during the path in acceleration from A' to A", to be lost.
It is an object of the present invention to overcome these drawbacks by producing an apparatus having the greatest efficiency in a reduced volume.